What do you guys do to condition your shins?
My instructor gave me a punching bag that's filled with sand and wood chips.  Are there any other safe alternatives?

I thought you were supossed to kick a bamboo tree until it falls down, a la Van Dam.

Bill3508 [smash]

Give a little sober thought to what you want to do here....hardening the body has a long-term price.

Muay Thai fighters are usually young farm boys with no future except to plant rice until they die...the fighting is their only way out, and thier careers are over before they're 35, so they don't care much.  You may have a different situation.
I was 4th dan Tae Kwon Do..twenty years...went for the hand conditioning big time when I was in my late twenties.  Pounded on cement blocks, hot gravel, the works.  I was hard, I was macho, I was bad.  Now I'm 54 and when I flex my hand it sounds like a bowl of Rice Krispies going off.  Weather changes, my hands hurt like hell.  Hurts to do a lot of stuff.  Bursa has been smashed and rebuilt so many times there's nothing but scar tissue where there should be soft, flexible stuff.  And nobody cares how many boards I could punch through thirty years ago.  I don't either.

It ain't worth it.

You don't condition your shins so much as desensitize the nerves and get used to the pain. Best thing you can do is let your shins heal properly after they are hurt.

Some guys roll coke bottles or pieces of bamboo up and down their legs,  kick sand bags, ect.. Kicking a regular heavy bag and sparring works for me. Just don't over do it.

bill,
Kicking a tree...no thanks! [:D]

Celt,
Thanks, I'll keep what you said in mind.  In thailand, they kick trees to purposely fracture their shins, so that when it heals, callus forms, thus making their shins harder.  I have no intention of going to that extreme, but thanks for the warning anyway. [:)]

Dungus,
Is it safe to roll things down your leg?  My instructor told me that it can cause a lot of bone growth problems, and that it kills nerves.  He told me that the only thing he would recommend was to kick heavy punching
bags, which is safe and hurts less than doing other things. [BD]

Well, my shins are all battered and dinged up, but you could almost break a 2x4 across them without me feeling much pain.

I owe it all to skateboards repeatedly shashing into my shins, so my answer is, take up skateboarding. [BD]

Before you start tearing up your shins with wood chips or kicking coconut trees I would ask how many times a day you are kicking a heavy bag or muay thai pads?  Preferably both. If your not kicking at least 1000 times a day per side plus 1000 ea of punches, elbows, knees and headbutts then you and your "instructor" should not be discussing "toughening up" your shins.  Once you do these things and run 5-10 miles a day,(for many months, if not years) then you may need to find some creative way to toughen up your shins before you do any full contact ring sparing.  Sometimes the one with the toughest shins wins.
Usually just training and practicing with partners will toughen up most peoples legs like baseball bats in just a few months.  The first time you "klak" shins with someone trying to muay thai kick you will be all the toughening up your shins will ever need.